An important feature in food casings, especially in sausage casings, is their peelability. The casings should adhere sufficiently firmly to the food in order that no fat can collect between the casing and the surface of the food. However, they should also not adhere too firmly, in order that they can be peeled off, without components of the food surface being torn out in the course of this. The adhesion depends strongly here on the type of food or sausage variety. For instance, blood sausage, for example, adheres particularly strongly to the casing. In addition, the type of ripening process (duration of ripening, temperature and atmospheric humidity during ripening) also has an influence on the adhesion. The material of the casing (regenerated cellulose, collagen, thermoplastic starch, etc.), optionally with a reinforcement of fiber paper, nonwoven or textile, is also of importance.
In the prior art, a multiplicity of impregnations and coatings are described for the various sausage types and casing types. The impregnations in this case contain adhesion components, release components or a combination of the two. Thus, casings for dry sausage should adhere sufficiently firmly to the sausage emulsion during the entire manufacturing period and also exhibit sufficient shrinkage in order that no creases form. For this purpose, reactive and non-reactive adhesion components have proved to be effective. Those that are suitable as non-reactive adhesion components are, for example, gelatin, casein or chitosan. The effect of the non-reactive adhesion components can be reinforced if they are crosslinked to the surface of the casing using at least bifunctional reagents, such as glyoxal or glutardialdehyde.
As reactive adhesion components, polyamide-polyamine-epichlorohydrin resins (DE 14 92 708) and urea or melamine/formaldehyde resins (EP 0 883 308; U.S. Pat. No. 3,378,379) have been used. Also, synergistically acting combinations of reactive and non-reactive adhesion components have also been described (EP 0 883 308, EP 2 140 765).
The impregnation with adhesion components can lead to an undesirable sticking together of the insides of the flexible-tube type casing. This can be reduced or suppressed by adding natural or synthetic oils, or fatty acids, in particular those having a chain length of 4 to 10 carbon atoms.
In order to facilitate the stripping of the casing after the end of the ripening process, various release components have been described with which the inside of the casing is impregnated. Here also, a distinction may be made between reactive and non-reactive components.
The non-reactive release components include ionic and nonionic polysaccharides and polysaccharide derivatives, in particular cellulose, cellulose ethers (methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, etc.), alginic acid or alginates (EP 0 502 431), starch and starch ethers (EP 0 006 551). This category also includes phosphoglycerides and fluorinated polymers such as polytetrafluoroethylene (EP 0 635 213).
Reactive peeling components are bound by covalent bonds to the material of the casing. Particularly effective peeling components have proved to be trivalent chromium fatty acid complexes (U.S. Pat. No. 2,901,358) and dialkyl ketenes having long-chain alkyl substituents (DE 14 92 699).
The effect of reactive and non-reactive release components can be further enhanced by combination with natural or synthetic oils (such as paraffin oil, silicone oil or MCT oil), fats or fatty acids or waxes (such as montan wax, beeswax or carnauba wax) (EP 0 180 207, DE 22 27 438, DE 34 47 026).
Internal impregnations with a combination of release components and adhesion components are also known. Thus, for example, in EP 0 676 143 (=U.S. Pat. No. 5,595,796) a combination of (i) a natural protein, an aminoplast precondensate or a polyamine/polyamide/epichlorohydrin resin and (ii) a chromium fatty acid complex or an alkyl ketene dimer is disclosed. A combination of cellulose ether and reactive resin, such as polyamine/polyamide/epichlorohydrin resin or a melamine/formaldehyde resin, is described in DE 28 53 269. EP 1 732 393 relates to a sausage casing having minimal emulsion adhesion, which casing is impregnated on the inside with a combination of a chromium fatty acid complex, a wax, a polyamine/polyamide/epichlorohydrin resin, a protein and/or an alkyl ketene dimer.
Despite the multiplicity of the previously proposed internal impregnations, until now no actually satisfactory solution has been found which meets all the requirements. Thus, blood sausages, raw sausages and sausage types of particularly lean meat exhibit very strong adhesion to casings made of biopolymers, in particular to casings based on cellulose. The peeled-off casing then frequently exhibits undesirable adhesions of sausage emulsion. In the case of foods having particularly low adhesion to the casing, the peeling components can, on the other hand, effect an unwanted detachment of the casing. In the resultant intermediate space, mold formation can then readily occur. Reactive peeling components, such as alkyl ketene dimers, additionally require a relatively long time period in order to react with the surface of the casing made of the biopolymers. The time period is additionally highly influenced by temperature and pH.
Non-reactive release components, such as cellulose ethers, are in addition readily extracted out by dissolution on soaking the casings. This leads later to an unsatisfactory or non-uniform adhesion of the casing. Anionic polyelectrolytes, such as carboxymethylcellulose and alginates, very readily form complexes with divalent ions, such as Ca2+ or Mg2+, which originate from the food. These complexes can then form undesirable gel-like deposits on the surface of the food. Many reactive adhesion components, but also many cellulose ethers, can stick the insides of the casing to one another, which considerably interferes with the stuffing operation.